LAM is developing several R&D activities for E-ELT instrumentation, in particular, different WFS concepts are investigated (Pyramid, ZELDA, a Zernike phase mask sensor, Phase diversity or still NL Curvature) and an ESO-EELT M1 mirror segment (1.5 m) has been demonstrated. Segmented mirrors are not only the solution for the problem of ELTs monolithic size but also for other questions related to fabrication, optics replacement and transport. And, they are widely used today for other applications: fiber coupling, LGS beam shaping, etc. Their only problem is how to assure the cophasing of segments to take advantage of the full optimum size. In the present work, we study the sensitivity to different WFS (Sack-Hartmann, Pyramid and ZELDA) to pupil phase discontinuity using a PTT mirror from Iris AO. Various test such as segment phasing, stability, saturation, flat, or still the addressing mode are then performed and compared.